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NZS 1170.5 Seismic Load Calculations

Using the SkyCiv Load Generator – NZS 1170.5 Seismic Load Calculations

The SkyCiv Load Generator now supports the seismic load calculation for New Zealand based on NZS 1170.5. With this addition, users can generate the seismic forces using the Equivalent Force method and the Design Response Spectrum which comes handy when applied to your S3D model. The data/map for major faults and hazard factor, \( Z \), in New Zealand had been digitized and converted to automate selecting these values based on the project address input. Users will be able to obtain get the following data from our server:

  • Hazard Factor \( Z \)
  • Nearest Major Fault
  • Distance from nearest major fault \( D \), in kms
  • Return Period Factor (ULS) \( R_{u} \)

Free users will be able to get these data but will only be able to calculate the seismic loads for a maximum of 3 solves per day. With a Professional Account or by purchasing the standalone Load Generator module, you can use all the features of this calculation as long as you want. You can purchase the standalone module thru this link.

Site Data

Together with the wind speed and ground snow load data, users can get the seismic parameters for the location obtained from our server by defining the “Required Annual Probability of Exceedance for Seismic” first and then the location:  

New Zealand Seismic Data

Figure 1. NZS 1170.5 additional parameter for obtaining site seismic parameters.

Seismic Parameters from SkyCiv Server

Figure 2. Site seismic parameters from USGS Web Services. Users can modify the parameters to obtain the most appropriate seismic load for the structure.

Structure Data

To calculate the seismic load for the structure, the structure data should be filled. Moreover, the required site seismic parameters in Site Tab should have values defined. These are: \( Z \), \( D \), \( {R}_{u} \), and Site Subsoil Class. By meeting these conditions, you can check the “Calculate Seismic Load” checkbox.  

Structure Seismic Parameters

Figure 3. Seismic parameters of the structure.

The seismic parameters needed to be defined are the following:

  • Largest Translational Period of the Structure \( T_{1} \) – used in Equivalent Force method
  • Structural Ductility Factor,  \( μ \)
  • Structural Performance Factor, \( {S}_{p} \)
  • Floor Weights – used for the vertical distribution of base shear in Equivalent Forces method. Data per level required are: Level (for designation), Elevation, and Weight

Users are free to edit this value which affects the corresponding calculated base shear for the structure.


Once all the parameters are defined, clicking the Generate Loads button will give a result as shown below.

Seismic Parameters used in Calculation

Figure 4. Seismic input parameters used in the calculation.

Design Response Spectrum

Figure 5. Calculated seismic forces using the equivalent force method and the generated design response spectrum.

Detailed Calculation

The detailed seismic load calculations can be accessed only by Professional account users and those who purchased the standalone load generator module. All the parameters and assumptions used in the calculation are displayed on the report to make it transparent to the user. You can download a sample detailed calculation thru this link.

Seismic Load Detailed Report

Figure 6. Detailed seismic load calculation generated from SkyCiv Load Generator.

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